RADIATION - HALF LIFE

FORENSIC SCIENCE PROJECT

Activity Objectives

During this activity you should be able to:

• Graph and describe the behaviour of radioactive decay
• Use a radioactive decay graph to determine the elapsed time of radioactive decay
• Use a radioactive decay graph to determine the mass of radioactive element left after a given period of time

Procedure

Radioactive Decay of Element X

• In the box provided is a sample of a radioactive material (or radioisotope) of element X.
• Each piece of paper in the container represents an atom of element X.
• The half life of this isotope is 20 days.
• Construct a table to record your results. Include the following headings on your table: Time in Half Lifes, Time in Days, Number of Atoms Decayed and Number of Atoms Left in the Sample.
• Shake the box long enough to mix up all the squares or "atoms" and spill the squares or atoms out onto the desk. (Careful, you must account for each square or atom).
• The squares or atoms which land on the desk with the marked side facing up have decayed during the that half life. Each time you do this decay procedure you will have replicated on half life.
• Set the decayed atoms aside and return the others back to the box. Repeat the decay procedure and record you findings six times. This represents 120 days.
• Graph the data you have collected. The horizontal axis of your graph should have the time and the vertical axis should show the number of atoms of element X left. Be sure to provide a title and the proper notations on each axis.
• Please return all the squares to the box when you have completed the activity

Reflections on the Activity

Answer the following question in your crime lab book

1. How many atoms of element X will be left after 50 days?
2. How long will it take for 40% of the atoms in your sample of element X to decay?

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